1. Field of the Invention
The present invention relates to an internal keratome apparatus and method of using the same to form a pocket between layers of a live cornea More particularly, the present invention relates to an internal keratome apparatus having a circularly-shaped reciprocating blade, and a method for using the same to form a circularly-shaped pocket between layers of a live cornea, and then expanding the pocket to form a flap-like layer at the front surface of the live cornea.
2. Description of the Related Art:
A normal ametropic eye includes a cornea, lens and retina. The cornea and lens of a normal eye cooperatively focus light entering the eye from a far point, i.e., infinity, onto the retina. However, an eye can have a disorder known as ametropia, which is the inability of the lens and cornea to focus the far point correctly on the retina. Typical types of ametropia are myopia, hypermetropia or hyperopia, and astigmatism.
A myopic eye has either an axial length that is longer than that of a normal ametropic eye, or a cornea or lens having a refractive power stronger than that of the cornea and lens of an ametropic eye. This stronger refractive power causes the far point to be projected in front of the retina.
Conversely, a hypermetropic or hyperopic eye has an axial lens shorter than that of a normal ametropic eye, or a lens or cornea having a refractive power less than that of a lens and cornea of an ametropic eye. This lesser refractive power causes the far point to be focused on the back of the retina.
An eye suffering from astigmatism has a defect in the lens or shape of the cornea. Therefore, an astigmatic eye is incapable of sharply focusing images on the retina.
In order to compensate for the above deficiencies, a technique known as photorefractive keratectomy has been developed which involves the placement of lenses in front of the eye (for example, in the form of glasses or contact lenses). However, this technique is often ineffective in correcting severe vision disorders.
An alternative to photorefractive keratectomy is surgery. For example, in a technique known as myopic keratomileucis, a microkeratome is used to cut away a portion of the front of the live cornea from the main section of the live cornea. That cut portion of the cornea is then frozen and placed in a cyrolathe where it is cut and reshaped. Altering the shape of the cut portion of the cornea changes the refractive power of this cut portion, which thus effects the location at which light entering the cut portion of the cornea is focused. The reshaped cut portion of the cornea is then reattached to the main portion of the live cornea. Hence, this reshaped cornea will change the position at which the light entering the eye through the cut portion is focused, so that the light is focused more precisely on the retina, thus remedying the ametropic condition.
Keratophakia is another known surgical technique for correcting severe ametropic conditions of the eye by altering the shape of the eye's cornea In this technique, an artificial organic or synthetic lens is implanted inside the cornea to thereby alter the shape of the cornea and thus change its refractive power. Accordingly, as with the myopic keratomileucis technique, it is desirable that the shape of the cornea be altered to a degree which enables light entering the eye to be focused correctly on the retina.
Laser in situ keratomileusis (LASIK), as described, for example, in U.S. Pat. No. 4,840,175 to Peyman, the entire contents of which is incorporated herein by reference, is a further known surgical technique for correcting severe ametropic conditions of the eye by altering the shape of the eye's cornea. In the LASIK technique, a motorized blade is used to separate a thin layer of the front of the cornea from the remainder of the cornea in the form of a flap. The flap portion of cornea is lifted to expose an inner surface of the cornea. The exposed inner surface of the cornea is irradiated with laser light and thus reshaped by the laser light. The flap portion of the cornea is then repositioned over the reshaped portion and allowed to heal.
In all of these techniques, it is critical that the incisions are made in the cornea in a very precise manner. Otherwise, the vision may not be corrected properly, and worse, severe damage to the eye may occur.
Accordingly, it is necessary that the cornea be prevented from moving while the cutting or separating of the corneal layers is being performed. Also, it is necessary to flatten out the front portion of the cornea when the corneal layers are being separated or cut so that the separation or cut between the layers can be made at a uniform distance from the front surface of the cornea. Previous techniques for flatting out the front surface of the cornea involve applying pressure to the front surface of the cornea with an instrument such as a flat plate. However, these techniques can cause damage to the eye, in particular, the pressure can cause fluid to leak out of the eye.
In addition to stabilizing the cornea when the cutting or separating is being performed, the cutting tool must be accurately guided to the exact area at which the cornea is to be cut. Also, the cutting tool must be capable of separating layers of the cornea without damaging those layers or the surrounding layers.
Furthermore, when the keratophakia technique is being performed, it is desirable to separate the front layer from the live cornea so that the front layer becomes a flap-like layer that is pivotally attached to the remainder of the cornea and which can be pivoted to expose an interior layer of the live cornea on which the implant can be positioned. It is therefore necessary that the cutting tool be accurately guided to form a suitable flaplike layer without damaging the surface onto which the implant is to be positioned. It is also necessary that the angle of the cutting is controlled so that the surface of the exposed interior layer is at a desired angle (e.g., normal) with respect to the optical axis of the eye.
Additionally, because the epithelium cells which are present on the surface of the live cornea may become attached to the blade when the blade is being inserted into the live cornea and thus become lodged between the layers of the live cornea, thereby clouding the vision of the eye, it is desirable to remove the epithelium cells prior to performing the cutting.
Examples of known apparatuses for cutting incisions in the cornea are described in U.S. Pat. No.: 4,298,004 to Schachar et al., U.S. Pat. No. 5,215,104 to Steinert, and U.S. Pat. No. 4,903,695 to Warner, the entire contents of which are incorporated herein by reference.
However, a continuing need exists for an improved apparatus and method for cutting a precise incision into a live cornea. A continuing need also exists for an effective and simple method of removing the epithelium cells from the surface of the live cornea prior to inserting a cutting tool into the live cornea.